Publication date: 15th May 2025
Recent studies have shown that inorganic semiconductor nanoclusters can be synthesized with a fibrous organic-inorganic mesophase and then assembled into chiral films through meniscus guided deposition. These films are capable of exceptional circular dichroism, displaying record g-factors up to 1.3 (g-factors are the figure of merit for chiroptics), and enormous domain sizes, greater than 6 mm2. The origin of these properties lies in the fibrous mesophase that holds the clusters in close proximity for exciton coupling, and allows them to be twisted to form a chiral arrangement. With this understanding we hypothesized that changing the ligand lengths in the mesophase matrix could alter their chiroptic response; decreasing the inter-cluster proximity should enhance their exciton coupling strength and as such their chiroptical signal, while increasing their spacing should have the inverse effect. To study this we created nanoclusters in mesophases composed of ligands with different chain lengths, and then measured the local CD values of both spin-coated and meniscus guided films using micron-resolution mapping at a synchrotron source with a Mueller Matrix Polarimeter. A histogram of the measured g-factors can then be fit with a gaussian distribution and the standard deviation taken as a measure of that ligands proclivity to form chiral structures. Interestingly, we find that there is a definitive trend with ligand length and the chiroptic g-factor but the trend is exactly opposite to our hypothesis, with longer ligands leading to enhanced chirality despite larger cluster-to-cluster spacing. While the cause of this inverted trend is unknown, our current simulations suggest this correspondence may originate from large length scale interactions generating a high degree of sensitivity to small angular changes in the pitch of these fibers, in which case increased flexibility of longer ligands could allow for tighter pitch and out scale any reduction in coupling strength. The results of this study will inform the community how best to design inorganic semiconductor nanocluster systems to maximize chiroptical signal and suggests that large gains are still within easy grasp.
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